The present invention relates to a safe measure for preventing the occurrence of a disaster which is ascribable to the motion of the movable part of an automatic machine such as an industrial robot.
Regarding an automatic machine, such as industrial robot or NC machine tool, wherein an object or a tool is moved to a target position given by a control signal, a dangerous situation arises when a person or the like is within the moving limits of a movable part during the operation of the automatic machine.
As to the industrial robot etc., there is a considerably high probability of the entry of a person into the moving limits of the movable part during a specified mode such as a teaching mode. Likewise, as to the NC machine tool etc., dangerous situations are liable to occur at the change of the tool or workpiece, etc.
The control system of such automatic machine, e.g., the industrial robot is often contructed as a servo control system empolying a computer. This control system includes therein the central processing unit of the computer, a servo control circuit at a posterior stage, a servo amplifier and a servomotor at posterior stages, etc.
In order to prevent the occurrence of the dangerous situation, there has heretofore been employed a method in which, when the industrial robot is set at the specified mode such as the teaching mode, a signal is supplied from the central processing unit to the servo control circuit, thereby to restrain the manipulated variable of the movable part such as a manipulator which is manipulated by the servomotor.
The prior-art example, however, has had the disadvantage of becoming quite useless as a safe measure when any fault arises in a portion extending from the servo amplifier to the servomotor, resulting in the runaway of the servomotor.